A&P Chapter 20 - Vessels and Circulation

If blood vessels don’t function properly…

blood borne substances don’t get to the body!

Tissue injury, metabolism is impaired, every body function is threatened

Artery

Carries blood away from the heart

Vein

Carry blood to the heart

Capillaries

Teeny tiny blood vessels with super thin walls that allow gas exchange to take place

Systemic arties

Provide oxygen rich blood to the body

Pulmonary arteries

Carry low-oxygen blood back to the lungs

Lumen

The hollow passage blood flows through

Arterial lumens vs venous lumens

Arteries have smaller lumens that help maintain blood pressure

Arteries have thicker walls and smaller diameters, so they look more rounded

Vasa vasorum

“vessels of the vessel”

Small blood vessels within the walls of larger blood vessels that provide nutrients and blood to the cells of the vessels, since blood moves too fast and through walls too thick to benefit from the nutrients

Pressure in arteries vs veins

Veins have much lower pressure, with thinner walls and larger diameters

Three layers of the vessels (inner to outer)

Tunica intima

Tunica media

Tunica externa

Tunica intima

Endothelium tissue

Damage to this layer signals the need for clots to form

Tunica media

Smooth muscle cells

Thickest artery layer

Contraction and relaxation controls the lumen diameter and therefor controls blood flow and pressure

Vasoconstriction

decreases blood flow

narrows lumens

increases blood pressurev

vasodilation

increase blood flow

widen lumen

drop blood pressure

Tunica externa

Collagenous and elastic fibers

Sheath

Thickest layer in veins

Help hold vessel in position regardless of movement

Elastic artery

Have tons of elastic that lets them expand and recoil depending on blood surges, managing blood pressureM

Muscular artery

Farther from heart, w less notable blood surges, smooth muscle in the tunica media increases

Thick tunica media means they play big roles in vasoconstriction, and they can’t really expand because they don’t have much elasticTh

Elastic vs muscular arteries

The line between elastic artery and muscular artery isn’t perfectly clear! It’s a gradual shift of few elastic and more muscle or vice versa

Arteriole

Very small artery leading to a capillary

Same three layers, but very thin

Since they’re so skinny, arterioles slow down blood flow and therefore cause a drop in blood pressure

They’re always a bit contracted, so they have a consistent muscular tone (vascular tone) like skeletal muscles have posture

Resistance!! Regulate blood pressure!!

Capillaries

Microscopic vessels that supply blood to tissue via perfusion

Exchange gasses directly between capillaries and surrounding tissue

It doesn’t have the same three layers because it needs to be leaky

Three types of capillaries

Continuous capillaries (tight junctions between cells, barely permeable)

Fenestrated capillaries (pores and also tight junctions. permeable to bigger molecules)

Sinusoid capillaries (big gaps, clefts, pores, permeable to big ass plasma proteins and cells.)

Venules

Capillaries lead into these

Multiple venules become veins

These have endothelium and an outer layer (very thin tunica externa)

What do veins have that arteries don’t? Why do they?

Valves!

Veins have to fight gravity and push push push blood back up into the heart. Then veins prevent backflow that isn’t such a risk in arteries

Where is excess blood stored if it’s not yet needed?

Veins! Blood resevoir!

Veins have well over half the blood at any time, because they distend well without leading to high blood pressuer

Blood pressure

force blood puts on the walls of the vessels or the chambers of the heart

Clinically, measured in mm Hg (millimeters of mercury) using the brachial artery.

Measured in a ratio of systolic pressure over diastolic pressure

Typical systolic pressure

higher number — 120 mm Hg

Represents arterial pressure resulting from ejection during ventricular contraction (when the least blood is in the heart, and most is in the arteries)

Typical diastolic pressure

lower number - 80 mm Hg

Represent arterial pressure of blood during ventricular relaxation (when the most blood is in the heart, and least is in the arteries)

Pulse

Expansion and recoiling of arteries after blood is ejected from the heart

Indirect measurement of heartrate

Five places you can feel pulse

Carotid artery (neck), brachial artery (arm), radial artery (wrist), facial artery (right under chin), temporal artery (temple)

First sound when measuring blood pressure indicates…

systolic pressure (blood flow returns to arm)

Second sound when measuring blood pressure indicates…

diastolic pressure (last sound you hear as blood flow returns to normal)

Five factors influencing blood flow and pressure

Cardiac output, compliance, blood volume, blood viscosity, blood vessel length and diameter

Any factor that causes cardiac output to increase…

will elevate blood pressure and increase blood flow

Compliance

Ability of a compartment to expand to accomodate increased content

Veins are more compliant than arteries

Three variables that determine blood flow

Radius of vessel

Blood viscosity

Length of blood vessel

What determines blood viscosity?

Formed elements

Plasma proteins

What are some conditions that could impact viscosity?

Anemia (lack of erythrocytes)

Liver abnormalities (since plasma proteins come from liver)

How does a shortened vessel affect blood?

Shorter vessels decrease resistance and increase flow

Vascular tone of a vessel

contractile state of smooth muscle

Primary determinate of diameter, resistance and flow

Increasing diameter does what to resistance?

Lowers resistance , decreases flow

Imagine the level of a river decreasing— less of it touches the walls

Hypertension

If the compliance is lower, and the diameter is smaller, there’s more reistance. The heart has to work hard to overcome resistance

Two reasons vein pressure is higher than atria (allowing blood to keep going from high to low pressure)

The pressure in the atria during diastole is SUPER low. It’s not hard to be higher than that!

The skeletal muscle pump and respiratory pump help keep the blood pushing through the veins.

What regulates vascular homeostasis?

The cardiovascular centers in the brain (they control both the cardiac and vascular functions)

The limbic and autonomic nervous systems also play roles

What are the three cardiovascular centers?

Cardioaccelerator centers - stimulate cardiac function, sympathetic stimulation

Cardioinhibitor centers - slow cardiac function, parasympathetic stimulation

Vasomotor centers - control vessel tone/contraction

Where are the vascular baroreceptors?

The aortic sinuses, the carotid sinuses

What do baroreceptors do when blood pressure is too high?

They’re stretched, so cardiac output has to slow (parasympathetic!)

Vasodillation

These together help blood pressure fall

What do baroreceptors do when blood pressure is too low?

They’re loose, so cardiac output has to speed up (sympathetic!)

Vasoconstriction

These together help blood pressure rise

When the body is more active…

oxygen levels fall and CO2 levels rise

More hydrogen is produced, so pH rises

What do chemoreceptors do when CO2 is high and pH is low?

They stimulate the cardioaccelerator and vasomotor centers

They increase cardiac output

What happens when the CO2 and pH levels are back to normal?

The cardioinhibitor center slows the heart back down

Catecholamines

Epinepherine and norepinephrine

The main hormones that control the cardiovascular system

Secreted by adrenal gland to increase heart rate and force.

Basically they handle fight or flight

Antidiuretic Hormone/Vasopression

Secreted when osmolarity increases, usually because blood loss

It tells the kidneys to reabsorb more water so the body holds onto all available fluids

Erythropoietin

Kidneys release it when blood flow or O2 levels decrease

Stimulates production of erythrocytes in bone marrow

Atrial Natriuretic Hormone

Secreted in the atria when blood volume is high enough for extreme stretching

Promote loss of sodium and water from kidneys, promoting fluid loss so blood volume drops

Pulmonary trunk

Vessel exiting the right ventricle, then bifurcates into the pulmonary arteries, which carry deoxygenated blood

Hepatic Portal System

Brings nutrients and certain wastes to the liver for processing

What organs have capillaries leading to the hepatic portal system?

Stomach, intestines, spleen

How does the liver receive blood?

The hepatic artery and hepatic portal vein

How does blood leave the liver?

Right, left, and middle heaptic veins, flowing into the inferior vena cava

Foramen ovale

In fetus, blood jumps from right to left atrium

Turns into the fossa ovalis

ductus arteriosus

Blood jumps from pulmonary trunk to aorta so there’s not too much blood in the developing lungs

Turns into the ligamentum arteriosum

Ductus venosus

Branches from umbilical vein so placenta blood can skip liver and go to the heart

Turns into the ligamentum venosum